Thus, the warning occurs because partition 1 starts at logical sector 63 = byte 32256, a number not divisible by 4096; in fact it's near the end of the 7th physical sector (position 7.875 to be exact :)

Should you fix it? If so, how? [always backup!]

In theory this sort of partitioning may affect read/write IO rates somewhat, depending on your drive's firmware. If you are happy with the performance now, ignore the warning, and no need to do anything. If not, backup all important data first, and then use Gparted to move the partition so that it starts at 4096-byte sector; setting the start boundary at 1 MiB is an easy way to do it.

Technically, you can set the start to any logical sector which is a multiple of 8, e.g. 64 is good, 256 is good, etc., but 63, 255... are not.

Select the storage device containing the erroneously sized partition from the pull-down menu in the upper right hand corner of the GParted menu.

Select the erroneously-sized partition by clicking on it in the rectangular partition map.

Now you may choose to delete and create a new partition or you may choose to resize the existing partition. Regardless of your choice you will reach a menu that allows you to set the size of the partition. You must clear the "Round to cylinders" checkbox and set the size of the free space preceding to 1MiB. It will look similar to